The quality of the surface of the workpiece is evaluated in a workpiece machined by a machine tool or the like. The quality of the surface affects not only the aesthetic appearance of the surface as seen by a person but also the design as seen by a person. For example, when the quality of the surface is poor, lines and patterns may be visible in undesired areas. In particular, when the object to be evaluated is a mold, the shape of the surface of the mold is transferred to many products manufactured. The shape of the surface of the mold is important, and it is preferable to increase the quality as seen by a person. The quality of such a surface can be evaluated by measuring the surface roughness or the like with a measuring instrument.
As a method for evaluating the quality of a surface, a method for evaluating the quality of the surface based on an image obtained by photographing the surface of the object is known. For example, there is known a method including photographing the surface of an object to generate image data, performing frequency analysis of a change in the brightness obtained from the image data, and performing evaluation based on a frequency component that can be visually recognized by a person (see Patent Literature 1 and Patent literature 2).